1. Field of the Invention
This invention relates to apparatus and methods for use in a wellbore to control the distribution of injected material in a wellbore. More particularly, the invention relates to methods and apparatus for providing a more uniform gravel pack in a wellbore.
2. Background of the Related Art
Hydrocarbon wells, especially those having horizontal wellbores, typically have sections of wellscreen comprising a perforated inner tube surrounded by a screen portion. The purpose of the screen is to block the flow of unwanted materials into the wellbore. Despite the wellscreen, some contaminants and other unwanted materials like sand, still enter the production tubing. The contaminants occur naturally and are also formed as part of the drilling process. As production fluids are recovered, the contaminants are also pumped out of the wellbore and retrieved at the surface of the well. By controlling and reducing the amount of contaminants that are pumped up to the surface, the production costs and valuable time associated with operating a hydrocarbon well will likewise be reduced.
One method of reducing the inflow of unwanted contaminants is through gravel packing. Normally, gravel packing involves the placement of gravel in an annular area formed between the screen portion of the wellscreen and the wellbore. In a gravel packing operation, a slurry of liquid, sand and gravel (xe2x80x9cslurryxe2x80x9d) is pumped down the wellbore where it is redirected into the annular area with a cross-over tool. As the gravel fills the annulus, it becomes tightly packed and acts as an additional filtering layer along with the wellscreen to prevent collapse of the wellbore and to prevent the contaminants from entering the streams of production fluids pumped to the surface. Ideally, the gravel will be uniformly packed around the entire length of the wellscreen, completely filling the annulus. However, during gravel packing, the slurry may become less viscous due to loss of fluid into the surrounding formations or into the wellscreen. The loss of fluid causes sand bridges to form. Sand bridges are a wall bridging the annulus and interrupting the flow of the slurry, thereby preventing the annulus from completely filling with gravel.
The problem of sand bridges is illustrated in FIG. 1, which is a side view, partially in section of a horizontal wellbore with a wellscreen therein. The wellscreen 30 is positioned in the wellbore 14 adjacent a hydrocarbon bearing formation therearound. An annulus 16 is formed between the wellscreen 30 and the wellbore 14. The Figure illustrates the path of gravel 13 as it is pumped down the production tubing 11 in a slurry and into the annulus 16 through a crossover tool 33.
Also illustrated in FIG. 1 is a formation including an area of highly permeable material 15. The highly permeable area 15 can draw liquid from the slurry, thereby dehydrating the slurry. As the slurry dehydrates in the permeable area 15 of formation, the remaining solid particles form a sand bridge 20 and prevent further filling of the annulus 16 with gravel. As a result of the sand bridge, particles entering the wellbore from the formation are more likely to enter the production string and travel to the surface of the well. The particles may also travel at a high velocity, and therefore more likely to damage and abrade the wellscreen components.
In response to the sand-bridging problem, shunt tubes have been developed creating an alternative path for gravel around a sand bridge. According to this conventional solution, when a slurry of sand encounters a sand bridge, the slurry enters an apparatus and travels in a tube, thereby bypassing the sand bridge to reenter the annulus downstream. The shunt tubes may be placed on the outside of the apparatus or run along the interior thereof. However, there are problems associated with both designs. For example, by being outside of the apparatus, the shunt tubes are susceptible to breakage or deformation during construction or placement of the wellscreen in the wellbore. Additionally, since the shunt tubes are on the outside, the overall diameter of the production apparatus is increased, thereby decreasing the diameter of the annulus, and decreasing the filtering capabilities of packed gravel.
Shunt tubes located inside an apparatus are limited in their internal diameter and are generally constructed with little cross-sectional volume. Shunt tube-type devices also typically provide one location for slurry to enter and one location for slurry to exit. The entry and exit apertures cannot be easily relocated or adjusted for conditions of formations downhole because they are pre-manufactured. For example, when a sand bridge is by-passed using one of these conventional designs, the slurry reenters the annulus where the shunt tube exits the apparatus. As a result, the slurry may reenter the annulus adjacent the same highly permeable, formation causing the liquid portion of the slurry to be lost into the formation and more sand bridges to be formed as a result of the increased viscosity of the slurry.
There is a need therefore, for a wellscreen having an alternative pathway for injected material to by-pass sand bridges or other obstructions in a wellbore. There is a further need therefore, for a wellscreen that diverts the flow of a gravel slurry to the interior of the wellscreen and, thereafter, redirect the slurry to the exterior of the screen at a predetermined location along the wellbore. There is yet a further need for a wellscreen that controls the reentry of the slurry by decreasing, increasing or closing apertures formed in a wall of the wellscreen. There is a further need therefore, for a wellscreen for use with gravel packing operations that provides a bypass for slurry wherein the bypass provides a channel of greater volume than prior art devices. There is yet a further need for a wellscreen for use with a gravel packing operation wherein the openings of apertures are resistant to erosion by high velocity particles.
The present invention generally provides for an apparatus for use in a wellbore having an alternative pathway for a slurry to by-pass an obstruction such as a sand bridge during gravel packing.
In one aspect of the invention, an apparatus includes a perforated base pipe, a wire wrap around the perforated base pipe and an annular space therebetween providing an alternative pathway for a slurry to by-pass a sand bridge. At least one aperture is formed through the wire wrap to provide a path for slurry into the apparatus and at east one aperture is formed through the wire wrap to provide a path back out of the apparatus. Another aspect, an apparatus additionally includes a second wire wrap around the first wire wrap and forming a second annular space in the apparatus to provide an alternative pathway for a slurry to by-pass a sand bridge.
In another aspect, the invention provides a method to control and predetermine the optimal exit point for the slurry to reenter the annulus from the alternative pathway of the apparatus. The method comprises collecting information such as geological surveys and tests of the wellbore to determine the type of formations that would be encountered down hole during production; analyzing the information; adjusting the size and/or plugging up the apertures of the screen with inserts based upon the collected information, and adding protective inserts to the apertures if highly abrasive particles are present in the wellbore. In yet another aspect of the invention, the apparatus does not include a base-pipe but only two tubular-shaped wire wraps with an annular space formed therebetween.